1. Field of the Invention
The present invention relates to a blow molded article and the method of making same. More particularly, the present invention is concerned with forming double wall reinforced vertical ribs into a blow molded vehicle bumper.
2. Description of the Related Art
It is known to manufacture lightweight bumpers from blow molded plastic material. However, current blow molded bumpers suffer the drawback of lacking effective blow molded structure for attachment of the bumper body to a vehicle frame member. Conventional blow molded bumpers generally include a series of fastening studs or bolts which are either molded into or surround the plastic. These studs are then used to affix the bumper to the vehicle frame. However, studs or bolts are difficult to incorporate into the mold and tend to pull away from the plastic material under relatively low tensile loads. The incorporation of stud plates or blind fasteners have only partially cured the mounting problem while adding undesirable weight and complexity to the bumper system.
Other bumper systems provide for molding structural members within the bumper body. An example of such a system is U.S. Pat. No. 5,271,650, which teaches a method of blow molding a bumper system having metal attaching members integrally molded therein. The attaching member is generally made of sheet metal and serves to affix the bumper to the vehicle. However, the integral molding of metal frame members requires a multiple step molding process. The mold cavity must first locate the attaching members and associated hardware prior to the actual blow molding process. These attaching members add undesirable weight and expense while defeating the simplicity of a wholly blow molded bumper.
It is therefore desirable to manufacture a wholly blow molded light weight bumper system which provides reinforced blow molded structure which adds to the overall rigidity of the bumper system. It is further desirable to manufacture a light weight bumper system which provides reinforced blow molded structure for mounting to a vehicle. It is still further desirable to manufacture a light weight blow molded bumper system which eliminates the use of blind fasteners while providing the opportunity to hide the vehicle mounting components within the bumper
Responsive to the disadvantages of the prior art, the present invention provides a wholly blow molded light weight bumper system providing double wall reinforced vertical ribs.
According to one embodiment of the present invention, a blow molded vehicle bumper system is disclosed. The blow molded vehicle bumper having a vertical reinforcement rib for attachment of the bumper to a vehicle frame member extending from a vehicle. The bumper extending substantially across the width of the vehicle and having a front side facing away from the vehicle and a back side facing toward the vehicle.
The blow molded bumper body formed of thermoplastic material providing a substantially uniform wall thickness and having a substantially horizontal parting line extending substantially across the length of the bumper. A recessed portion formed into the bumper backside and being defined by a substantially horizontal top portion and a substantially horizontal bottom portion. The vertical rib integrally formed into the recessed portion and joining the top portion and bottom portion The vertical rib having a reinforced double wall thickness of thermoplastic material pinched together and projecting toward the vehicle and oriented substantially perpendicular to the parting line.
The vertical reinforcement rib comprises thermoplastic material pinched together. When the thermoplastic material is pinched between a first surface and a second surface the material is folded over itself creating a double wall of thermoplastic material. Compressing the material between the surfaces aids the fusing of the material layers and the forming of a double-wall strong vertical reinforcement rib.
The present invention further teaches a method of blow molding a vehicle bumper having ribs perpendicular to the parting line. A mold apparatus is provided having first and second molds defining an interior surface. A first surface projects from one of the molds and is perpendicular to the first and second molds. In association with the first surface a second surface is movable between a retracted position and an extended position. The second surface extends toward the first surface during extension and away from the first surface during retraction. Extruding a thermoplastic parison substantially between the first and second molds when the mold is in the open position and then closing the molding apparatus and containing the parison between the first and second molds. The parison is then inflated until the parison contacts the mold interior surface. The first surface is then extended from the retracted position and the thermoplastic parison is pinched therebetween. The pinching thereby forming a rib generally perpendicular to the first and second molds. The first surface is then retracted to release the rib formed in the extending step. Finally, the molding apparatus is opened and the article is released.
In another embodiment of the present invention both the first and second surface are movable to pinch the thermoplastic material between the first and second surfaces to create a double wall reinforced rib perpendicular to the first and second mold halves.
Accordingly, an object of the present invention is to provide integral mounting structure which adds to the overall rigidity of a bumper system. An advantage of the present invention is the use of blow molded vertical ribs to create a cross-brace perpendicular to the parting line thereby operating as an xe2x80x9cIxe2x80x9d beam like structural member. The vertical rib either alone or in multiples are therefore operable as integral structural members to readily mount and support the bumper body on a vehicle frame member.
These and other desired objects and advantages of the present invention will become more apparent in the course of the following detailed description and appended claims. The present invention may best be understood with reference to the accompanying drawings wherein illustrative embodiments are shown.